Fetching related model entries of all related entries

I am trying to make a twitter clone. Thanks to the wonders of MVC, after setting up the models relationships getting related entries has become really simple. For instance, getting all the posts of a single user for the users page is as simple as:

$posts = $user->getPosts();

I have run into a problem when I got to the homepage part where I'm supposed to show all the latest posts of the followed users. I can get all the followed users:

$followers = $user->getFollowers();

But what I need is the next step, all their posts. Something along the lines of:

So basically after getting all followers you can create some array of ids of those follower and then just find posts where follower id IN this array. Also think about selecting data you only need, and working on arrays(lower memory consumption, faster) etc.